Short circuit detector



March l H. P. MANLY SHORT CIRCUIT DETECTOR Filed July 14, 1954 Patented Mar. 10, 1936 UNITED STATE ATENT OFFICE SHORT CIRCUIT DETECTOR Harold P. Manly, Wilmette, Ill.

Application July 14, 1934, Serial No. 735,233

6 Claims. (Cl. 250-27) The invention relates to improvements in apas shown in circuits I4 and I5 and whereby paratus for detecting short circuits in electronic either or both of said branch circuits may be tubes and has for its object the provision of a opened or closed as desired. A heating circuit simple apparatus of the character indicated I9 including the tube cathode and a battery 20 which is capable of economical production and is arranged as indicated for heating the cathode 5 is highly eicient in use. of the tube substantially to its normal operating Another object of the invention is the provitemperature. sion of a simple apparatus of the character in- The tube to be tested is inserted in the circuits dicated especially adapted for use in testing I4, I5 and I9 as indicated, the switches I6, I1 l0 thermlonic radio tubes. and I8 being left open and a source of direct l0 Another object of the invention is the prov- Current Supplied t0 the ClCuit l0. A Current sion of apparatus of the character indicated will i'low in the circuit I6 entirely independently which is capable of use in testing such tubes of the branch circuits I4 and I5 and controlled under substantially normal conditions of use and only by the resistance or other impediments to without disturbance or interference from such current ow directly incorporated in said circuit 15 conditions. I0. This current flow may be read on the indi- Other objects will appear hereinafter. cator II and a note made thereof. If there is The invention consists in the combinations any short circuit in the tube being tested, the and arrangements of parts hereinafter declosing of switches I6, II and I8 will cause scribed and claimed. change in the reading of the indicator II.` Thus, 20

The invention will be best understood by referif switches I6 and I'I are closed, and there should ence to. the accompanying drawing forming a exist a short circuit between the tube plate and part of this specification and in which: the grid, this short circuit will complete and Fig. 1 is a diagrammatic view of a simple form close the branch circuit III, thereby establishing Of apparatus embOdYing the invention and a circuit in parallel with the resistance coil I3 25 shown in condition for testing an ordinary therand affording a path for current around said mionic radio tube; resistance coil, such parallel path of current Fig. 2, a similar View of a similar but slightly thereby materially reducing the total effective modified form of such apparatus; resistance in the circuit I0, causing an increase Fig. 3, a similar view showing the apparatus of current flow therein and thereby a change 30 as in use with an alternating current as the in the reading of the indicator II. If switches testing current; II and I8 are closed, with switchk I6 open, if

Fig. 4, a similar view showing a modified form there is a short circuit between the tube cathof application of the invention whereby the ode and grid, a parallel circuit will be provided o5 Same may be incorporated in apparatus for around both the resistance con I2 and the indi- 35 performing Othe` teStS Orl the tube; and cator II, thereby materially decreasing the flow of Fig. 5, a View similar to Fig. 4, but showing current through the indicator so that such change how a single indicator may be advantageously of reading of the indicator will show a short employed instead of the two indicators shown circuit between the cathode and grid of the tube. i0 in Fig. 4. If switches I6 and I8 are closed while switch I1 40 The embodiment of the invention illustrated is left open, any short circuit between the cathode in Fg- 1 COmDISeS a testing Circuit l0 rleludand plate of the tube will form a parallel circuit ins a Source of direct Current, an indicator Il, with reference to both resistance @011s l2 and I3 and two resistance coils I2 and I3 which serve, and the indicator II, thereby materially deaS Will be readily undelStOOd, as impediments or creasing the flow of current through the indicator 45 limitations to the normal flow in the testing cirand thus showing such short circuit. cuit, as will be readily understood by those 1f 3,11 three of the Switches I6, I'I and I8 are skilled in the art. Co-operating with the testclosed and there is any change in current flow ing circuit I0 are two branch Circuits I4 and indicated by the indicator H, this will show that I5,the branch circuit Hi including the resistance there is some short circuit defect in the tube 50 coil I3 and the plete and grid of the thermionic and the above tests may then be performed to tube t0 be tested- SS ShOWIl- The bTeIlCh CilCut locate where the short circuit is if such specific I5 includes the resistance coil I2 and the grid location is desired. By this arrangement it will and cathode or lament of the tube being tested, be noted that the tube cathode or lament is as shown. Switches I5, il, and i8 are included heated and at the same time maintained posi- 55 tive with reference to the other electrodes, or conversely, the other electrodes are maintained negative with reference to the heated cathode. As a heated cathode in a thermionic tube will carry an electronic current only when it i's negative with reference to one or more of the other electrodes, or conversely, when one or more of the other electrodes is positive with reference to the cathode, this arrangement will effectively prevent any electronic now through the tube during the test, and thereby prevent interference with theaccuracy of said test due to normal electronic iiow in the tube.

The modication illustrated in Fig. 2 is precisely the same as that illustrated in Fig. 1 eX- cept that spring-held switches 20, 2| and 22 are provided in the branch circuits I4 and I5 whereby said branch circuits will be held normally closed and the tests will be performed by simply operating one or all of said switches to open said branch circuits. Obviously, any change of current flow caused by opening any one or all of said switches, will indicate that there is some kind of a short circuit in the tube. If desired, the specific location of such short circuit may be then determined by successively opening the different switches.

The modified arrangement illustrated in Fig. 3 is such that an alternating current may be used in the testing circuit I0. For this purpose a rectier 23 is inserted as indicated in the branch circuit I5 and will thus serve to maintain the tube cathode constantly positive with reference to the other electrode so as to prevent any electronic ow through the tube during the various tests.

In this case also, any change in the current ow in the testing circuit I Il caused by the opening or closing of any of the switches I6, I'I and I8 will indicate that there is a short circuit in the tube and the location of such short circuit may be determined, if desired, as above.

In the modication illustrated in Fig. 4, twothrow switches 24 and 25 are arranged. in the branch circuits I4 and I 5 as shown. A plate circuit 26 is arranged as shown to be opened and closed by the switch 24 and includes a source of plate voltage 21 and another current indicator 28. A grid circuit 29 is also arranged to be opened and closed by the switch 25 and includes also a source of grid voltage and the indicator 28. By this arrangement when the switches 24 and 25 are manipulated to open and close the branch circuits I4 and I5, the tube may be tested just as in the apparatus illustrated in Fig. 1. When the switches 24 and 25 are manipulated to close the circuits 26 and 29, said circuits may be utilized for testing the qualities of the tube in other respects, the indicator 28 serving to indicate conditions in circuits 26 and 29, as will be readily understood by those skilled in this art.

The modication illustrated in Fig. 5 is the same as that illustrated in Fig. 4 except that the indicator II is moved into the cathode connection so as to serve as a common indicator for all the circuits, thus dispensing with the necessity of employing two indicators as illustrated in Fig. 4. Otherwise the arrangement is the same as that illustrated in Fig. 4 except that a supplemental switch 30 is provided in circuit I so that circuit Il) may be opened when the circuits 26 and 29 are being utilized.

By this arrangement a short circuit detector may be incorporated with other usual and normal testing circuits for the tube without undue or material modification of parts.

While I have illustrated and. described the preferred forms of construction for carrying the invention into effect, these are capable of wide variation and modification without departing from the spirit of the invention. I, therefore, do not wish to be limited to the precise details disclosed but desire to avail myself of such variations and modifications as fall within the scope of the appended claims.

I claim:

1. A short circuit detector for thermionic tubes comprising means for heating the tube cathode; a testing circuit including a source of suitable current, a plurality of impediments to current ow and an indicator; means for establishing a branch circuia in parallel withv each of said impediments and including two of the tube electrodes; and means for preventing electronic flow between said electrodes.

2. A short circuit detector for thermionic tubesV comprising means for heating the tube cathode; a testing circuit including a source of suitable current, a. plurality of impediments to current flow and an indicator; means for establishing a Yflow and an indicator; means for establishing a branch circuit in parallel with each of said impediments and including two of the tube electrodes; means for preventing electronic iiow between said electrodes; and means for opening and closing said branch circuits.

4. A short circuit detector for thermionic tubes comprising means for heating the tube cathode; a testing circuit including a source of suitable current, a plurality of impediments to current ilow and an indicator; means for establishing a branch circuit in parallel with each of said impediments and including two of the tubeelectrodes; means for maintaining the tube cathode positive with reference to the other electrodes and thereby preventing electronic flow between said electrodes; and means for opening and closing said branch circuits.

5. A short circuit detector for thermionic tubes f having cathodes, plates and grids, comprising means for heatinga tube cathode; a` testing circuit including a source of suitable current, a plurality of impediments to current ow, and an indicator; means for establishing a branch cir-l cuit in parallel with one of said impediments and including the tube plate and grid; means for establishing a second branch circuit in parallel with another of said impediments and including the tube grid and cathode; means for preventing electronic i'low between said electrodes; a plate circuit including a source of plate voltage, the tube plate, the tube cathode and the indicator in said testing circuit; a grid circuit including a source of grid voltage, the tube grid and the tube cathode; a two-throw switch arranged to open and close the plate-grid branch circuit and the plate circuit; and a two-throw switch arranged to open and close the cathodegrid branch circuit and the grid circuit.

6. A short circuit detector for thermionic tubes having cathodes, plates and grids, comprising means for heating a tube cathode; a testing circuit including a source of suitable current, a plurality of impediments to current flow, and an indicator; means for establishing a branch circuit in parallel with one of said impediments and including the tube plate and grid; means for establishing a seco-nd branch circuit in parallel with another of said impediments and including the tube grid and cathode; means for maintaining the tube cathode positive with reference to the other electrodes and thereby preventing electronic 110W between said electrodes; va plate circuit including a source of plate Voltage, the tube plate, the tube cathode and the indicator in said testing circuit; a grid circuit including a. source of grid voltage, the tube grid and the tube cathode; a two-throw switch arranged to open and close the plate-grid branch circuit and the plate circuit; and a two-throw switch arranged to open and close the cathode grid 10 branch circuit and the grid circuit.

HAROLD P. M ANLY. 

